OrbitalHub

On Thursday afternoon at 14:00 CEST, a stack of four spacecraft modules that left Earth on an Ariane 5 in October 2018 will, very briefly, become three and then two. ESA’s Mercury Transfer Module is scheduled to detach from BepiColombo’s two science orbiters as the mission’s controllers at the European Space Operations Centre in Darmstadt look on, with the first signal from the freed composite expected back on Earth by 15:53 CEST if everything goes to plan (ESA, 27 August 2026). After eight years and nine gravity assists, the part of the spacecraft that made the trip possible is no longer needed, and the part that has to do the science is, ungainly and for the first time, on its own.

Getting to Mercury is the kind of orbital mechanics problem where the obvious solution is forbidden. Falling toward the Sun does not slow a spacecraft down; it speeds it up, pulled by solar gravity, so the usual chemical-brake trick used at Mars is not enough to be captured into orbit around the smallest planet. BepiColombo has to match Mercury’s velocity almost exactly, and that takes far more energy than reaching even the distant gas giants. The mission’s answer was to spend years bleeding speed against an ion engine instead of staging a single dramatic burn, and the upcoming separation is the moment the engine is, finally, switched off and thrown away. As ESA’s mission manager Santa Martinez put it to Euronews on 1 September, “Mercury is a challenging destination. It’s very difficult to reach, it’s very difficult to operate there.”

Why a separation matters this much, and why the next two months are unusually tense, comes down to what changes about the spacecraft on Thursday. For the cruise the four modules sat one on top of the other inside a tight stack, with their instruments and cameras physically blocked from space by the boxy MTM at the base. Once the MTM floats off, the upper composite begins an entirely new mission with an entirely new thermal and radiation budget. Solar flux near Mercury is roughly ten times what it is near Earth, and the MTM had been there partly to shield the orbiters during the inner solar system transit. The flight director, Ignacio Tanco, has described the moment to Euronews as working “with a very hot pizza oven running right on your back” and “on a knife edge,” because the MPO’s solar panels have to be tilted within fractions of a degree of the Sun. Push them slightly away and the spacecraft starts losing power; angle them slightly closer and they start to bake. There is no second chance to find the right pointing before the thermal balance tips.

The spacecraft itself carries a long memory. BepiColombo launched on Ariane flight VA245 from Kourou on 20 October 2018 and reached escape velocity the same day, then spent almost exactly eight years climbing and falling through the inner solar system using four QinetiQ T6 ion thrusters on the MTM, with a maximum combined thrust of about 290 millinewtons, the most powerful ion engine array ever operated in space. The cruise used one Earth flyby in April 2020, two Venus flybys in October 2020 and August 2021, and six Mercury flybys between October 2021 and January 2025, the last of which imaged the permanently shadowed north polar craters Prokofiev, Kandinsky, Tolkien and Gordimer. The mission’s overall cost is estimated at 1.65 billion euros, and the arrival has already slipped about eleven months from its original December 2025 date because of a power-related anomaly that limited the available thrust before the fourth Mercury flyby in September 2024. On 15 June 2026 at 13:24 UTC the MTM’s solar electric propulsion was switched off for good, and from then on the mission is ballistic: BepiColombo is, in engineering language, “weakly captured” by Mercury’s gravity and following a free-falling trajectory through space.

What happens after 3 September is a sequence of three distinct steps rather than one event. From the separation through late November, the MPO and Mio remain mechanically and electrically joined, with the Magnetospheric Orbiter Sunshield and Interface (MOSIF) still attached, and the two orbiters fly free of the propulsion module for the first time in their lives. Then, between late November and early December 2026, a series of chemical thruster burns raises the orbit’s apocentre and lets Mercury’s gravity do the rest, putting the composite into polar orbit. Once captured, MPO and Mio separate from each other and head to their distinct orbits, MPO in a lower polar orbit for surface and interior science and Mio in a higher polar orbit at 590 by 11,640 kilometres for magnetospheric work. Engineers then spend roughly four months commissioning instruments on both orbiters, and only in April 2027 does the dedicated science campaign begin. The waiting list, when it eventually opens, is unusually long. Mercury’s iron core makes up roughly sixty percent of the planet’s volume, and the mission’s principal question is why a planet that small should pack such a dense metallic interior, and what that interior is doing to the unexpectedly long-lived magnetic field that makes Mercury (along with Earth) the odd rocky planet out. The two orbiters will “taste” the planet’s tenuous exosphere of hydrogen, helium, oxygen, sodium, potassium and calcium at the same time that MPO maps the surface, measuring surface temperatures down to a few hundred metres per pixel and sounding the crust with the RIME ice-penetrating radar that was deployed once in 2023 and has waited seven years to be used on Mercury. Separation on Thursday is the first of a small handful of moments that decide whether any of that science happens, and it is the one the ESA team can already see clearly. After MTM separation, mission controllers listen for the post-separation acquisition of signal and then go through the first health checks. If the composite is in the expected attitude, the high-gain antenna locking on Earth, and the temperatures inside the expected range, MPO and Mio spend the next three months coasting together in what ESA calls a Mercury approach configuration, conservatively waiting for the November capture window. The MTM, the workhorse that brought them there, has no attitude control after separation, so ESA’s flight dynamics manager Frank Budnik has been clear that “you cannot control it, you cannot manoeuvre it,” and the module will begin to tumble away in its own orbit past Mercury rather than around it. After eight years, the most powerful ion engine array ever flown is, for a few million kilometres at least, just a derelict tumbling through interplanetary space with the Sun in its face and no way to turn around.

The Soyuz MS-28 spacecraft touched down on the Kazakh steppe at 5:27 a.m. local time on Sunday, July 26, 2026, with three crew members strapped into a descent module that had just survived a 7.6 km/s hypersonic dive through the atmosphere. By the time the capsule rolled to a stop about 147 km southeast of Dzhezkazgan, NASA’s Chris Williams, Roscosmos’s Sergey Kud-Sverchkov, and Sergei Mikaev had spent 241 days in orbit and crossed 3,856 orbits of the Earth, roughly 164 million kilometers of free fall, longer than the average round-trip distance from Earth to Mars (NASA, July 2026).

The Soyuz landing sequence has not changed meaningfully since 1967. The capsule separates from its orbital and service modules, fires a braking engine, falls semi-ballistically for about seven minutes through 1,500 °C plasma, deploys two drogue chutes and a 1,000-square-meter main, jettisons its heat shield, and fires six solid-fuel soft-landing engines about 70 cm above the steppe (Energia/RussianSpaceWeb, 2024). Every crew member who has flown on a Soyuz, from the first 1967 boilerplate to Williams’s 2026 flight, has come home in essentially the same hardware lineage. No other crewed spacecraft has logged more return flights to Earth.

That continuity is narrowing. The U.S. Deorbit Vehicle (USDV), a heavily modified Cargo Dragon with 46 Draco thrusters and roughly 16 tonnes of propellant, is scheduled for delivery readiness in October 2028, with launch around mid-2029, after which the 420-tonne ISS will be steered into the Pacific at Point Nemo no earlier than late 2030 (NASA Office of Inspector General, 2025). Every Soyuz landing between now and then is one of the last acts of a 30-year joint occupation of low Earth orbit. On July 26, Expedition 74 ended; Expedition 75, with Jessica Meir in command and Anil Menon freshly arrived on Soyuz MS-29, took over.

Williams, a medical physicist by training, became the 642nd person to enter orbit when Soyuz MS-28 launched on Thanksgiving Day, November 27, 2025, from the Baikonur Cosmodrome. He and his two Russian crewmates joined Expedition 73/74 and spent eight months supporting more than 200 experiments, including semiconductor crystal growth, bioprinting of vascular tissue for cancer research, and testing a new European exercise device called the E4D that combines cycling, rowing, and resistance in one frame (NASA, March 2026).

The handover began on July 14, when Soyuz MS-29, carrying NASA astronaut Anil Menon and Roscosmos’s Pyotr Dubrov and Anna Kikina, docked at the Prichal node module after a three-hour rendezvous. Twelve days later, on July 25, Kud-Sverchkov passed command of the ISS to Meir. The next morning at 3:03 a.m. EDT, MS-28 undocked from the Rassvet module. For about two and a half hours, it drifted away in free fall, trailing by roughly 12 m/s of relative velocity, while ground controllers computed the deorbit burn.

At 5:32 a.m. EDT, the KTDU-35A main engine fired for 282 seconds, slowing the spacecraft by 115 m/s, enough to drop its perigee into the upper atmosphere. Twenty-two minutes later, the habitation and instrument modules separated, leaving only the 2.9-tonne descent module pointed heat-shield-first at an entry interface around 99.7 km. For the next six minutes, the capsule was silent through ionized plasma blackout as it bled off orbital velocity through friction alone.

The drogue chutes unfurled at 10.8 km, slowing the capsule from about 230 m/s to roughly 80 m/s, then the main canopy deployed at 8.5 km and trimmed the descent to a stately 6–7 m/s. The heat shield was jettisoned at 5.5 km, exposing the six solid-fuel soft-landing engines. At 0.7 m above the steppe, the Kaktus altimeter fired them, cutting touchdown speed to about 1.5 m/s. The capsule tipped onto its side, the way Soyuz always does. Recovery teams in Mi-8 helicopters reached the site within minutes. Williams was extracted, given a matryoshka doll with his face, and flown by helicopter to Karaganda before boarding a NASA aircraft back to Houston.

The Soyuz landing is a physics exam compressed into 24 hours of flying. Three constraints drive the design.

First, the lift-to-drag ratio of the descent module is intentionally low (about 0.3 to 0.4), achieved by offsetting the capsule’s center of mass. This generates just enough lift to steer the trajectory and trim peak deceleration to roughly 4 g during a guided reentry, instead of the 8 to 9 g the crew would experience in a fully ballistic descent. When something fails, as it did on Soyuz TMA-1 in 2003, TMA-10 in 2007, and TMA-11 in 2008, the capsule rolls at high speed to wash out the lift vector and falls steeply, sometimes hundreds of kilometers off-target. The lower L/D also caps heating at 150 to 200 W/cm², which is why the ablative shield can be phenolic resin and silica-fiber blanket rather than reusable tiles.

Second, the propulsion system is split. The KTDU-35A main engine, burning UDMH and nitrogen tetroxide (N₂O₄), lives on the service module and is jettisoned before entry. It provides the 115 m/s Δv for the deorbit burn. The six DMP soft-landing engines are solid-propellant, total mass around 60 kg, hidden under the heat shield, fire only once. From Tsiolkovsky’s rocket equation, the deorbit Δv comes out as:

Δv = v_e * ln(m_0 / m_f)

For the KTDU-35A, with a vacuum specific impulse near 315 seconds (v_e ≈ 3,090 m/s), losing 2.9 of the spacecraft’s roughly 7.2-tonne stack mass produces the needed 115 m/s. The math is forgiving; the margin lives in the parachute system.

Third, the parachute system is redundant by design. Two pilot chutes extract a 24 m² drogue, which pulls out a 1,000 m² main canopy. A separate 500 m² reserve canopy is packed independently in case the main fouls. The main weighs about 110 kg and inflates in roughly 1.5 seconds, producing a peak shock load of about 4–5 g.

The Kaktus altimeter deserves a separate mention. Older Soyuz used a cesium-137 source firing downward through a collimator, counting backscattered gamma rays from the soil; modern variants use sealed cobalt-60 in a redundant design. When the count rate climbs above a threshold at about 0.7 m altitude, it triggers the soft-landing engines. The system is mechanical-electronic, not radar, which is part of why Soyuz landings are timed to the second regardless of weather.

By the time the USDV fires its 46 Draco thrusters to drop the ISS into the South Pacific in 2030 or 2031, Soyuz will have completed more than 175 crewed flights and brought more than 500 people home from orbit. The descent module that carried Williams, Kud-Sverchkov, and Mikaev to the Kazakh steppe on July 26, 2026 is a direct descendant of the capsule that killed Vladimir Komarov in 1967. The parachutes are bigger, the altimeter is better, and the crews wear Sokol pressure suits, but the compromise is the same: trade g-load and landing accuracy for simplicity, redundancy, and a soft landing where helicopters can find you.

Expedition 75 now has a seven-person crew and a packed manifest through spring 2027, with a commercial rotation arriving in September aboard Crew-13. The station’s end is on the engineering calendar, but the landing sequence that has defined how humans come home from orbit will outlive it.

Sources: NASA Space Station blog (July 26, 2026); NASA media advisory (July 27, 2026); RussianSpaceWeb Soyuz landing systems reference (Energia, 2024); NASA Office of Inspector General report on USDV (IG-25-001, 2025); Soyuz MS-28 and MS-29 mission press kits (Roscosmos, 2025–2026). Photo credit: NASA/Bill Ingalls.

A small, jagged rock tumbling through space about 20 million kilometers from Earth just had its portrait taken. On July 6, 2026, the China National Space Administration released the first close-range images of (469219) Kamoʻoalewa, captured by the Tianwen-2 spacecraft from roughly 20 kilometers away on July 2. The pictures are grainy, low-resolution, slightly fuzzy at the edges. They are also the only close-up views humans have ever gotten of Earth’s most stable known quasi-satellite, and they sharpen a debate that has dragged on for nearly a decade about where this object came from. The rock’s elliptical path around the Sun takes it between roughly 0.1 and 0.3 AU closer and farther from Earth’s orbit, depending on where in the multi-decade cycle you sample it. From a ground-based telescope on any given night, Kamoʻoalewa is a faint dot moving against the stars: too small for any existing instrument to resolve as a disk, but bright enough that sensitive CCDs can pin down its spectrum and its rotation period. Both numbers have mattered for the past decade’s argument.

Kamoʻoalewa (a Hawaiian name meaning “oscillating celestial object”) was discovered in 2016 by the Pan-STARRS survey at Haleakalā Observatory in Hawaii (JPL Small-Body Database). Estimates put it somewhere between 16 and 40 meters across, it rotates once every 27 minutes, and it shadows Earth in a peculiar gravitational dance. Not a true moon, but a small body trapped in a 1:1 mean-motion resonance with our planet, looping the Sun in an orbit nearly identical to ours. From Earth’s perspective, the rock traces a slow, bean-shaped path that drifts between leading and trailing horseshoe configurations on timescales of decades. For at least the past hundred thousand years, give or take an order of magnitude, it has been Earth’s quiet companion. At some point it will leave.

For most of that history, nobody could get close enough to study it. Ground-based spectroscopy showed a spectrum that resembled space-weathered lunar regolith, with a weak 1.0 μm absorption band and a steep red slope that closely matched samples returned by Apollo 14 and the Chang’E-5 lander (Zhang et al., Nature Communications, May 2026). That match suggested the asteroid might be a piece of the Moon, blasted off by a relatively recent impact and gently nudged into a co-orbital path. But other groups showed that heavily weathered LL chondrite powder could produce a similar spectrum, and a Flora-family origin in the main belt remained plausible. Without a sample in hand, the question stayed open.

Tianwen-2 launched on May 29, 2025 from the Xichang Satellite Launch Center on a Long March 3B rocket, carrying 11 scientific instruments and a sample-return capsule designed for two distinct collection methods: a Hayabusa-style touch-and-go to grab regolith kicked up by a small thruster pulse, and an anchor-and-attach approach using robotic arms to clamp onto boulders and retrieve larger fragments. The spacecraft’s primary target was Kamoʻoalewa; an extended mission will later send it onward to main-belt comet 311P/PANSTARRS using a lunar gravity assist, with arrival in 2035.

The cruise phase took just over a year. Tianwen-2 first detected Kamoʻoalewa on June 6, 2026 at a range of 30,000 kilometers and refined the asteroid’s ephemeris from kilometer-scale uncertainty down to tens of meters (CNSA, July 2026). By June 19 it had closed to 2,000 km. Two weeks later, the framing camera returned the first resolved frames: a small, asymmetrical, jagged fragment, rotating visibly between exposures. The shape, in early analysis, looks more like a single competent block than the loose rubble pile some pre-arrival models had predicted.

The clincher will be the samples themselves, scheduled for collection later this year and return to a landing site near Jiuquan in late 2027. Tianwen-2 is the third mission in a decade-long run of asteroid sampling attempts, after JAXA’s Hayabusa2 (returned 5.4 g from Ryugu in December 2020) and NASA’s OSIRIS-REx (returned 121 g from Bennu in September 2023). Both of those targets were bigger than this one — Ryugu at about 900 m, Bennu at about 500 m — and both had escape velocities of tens of centimeters per second. Tianwen-2 is operating at a scale where escape velocity drops to a few centimeters per second, which puts the spacecraft closer to the asteroid in gravitational terms than a hang glider is to a hillside.

A new Nature Communications paper from Zhang and colleagues, published May 27, 2026, lays out what Tianwen-2’s near-approach spectroscopy already tells us about composition. The body’s reflectance spectrum matches the Itokawa-like LL chondrite class but with deeper space-weathering features than Hayabusa2 saw on its target. That tilts the evidence away from the lunar-ejecta hypothesis and toward a main-belt origin, but does not settle it. Samples in hand will.

Sampling on a 27-minute rotator is not trivial. A touch-and-go sequence has to compensate for the asteroid’s rotation, surface translation, and the very weak gravitational field — escape velocity from a 27-meter rocky body is on the order of a few centimeters per second. The Tsiolkovsky rocket equation, Δv = v_e * ln(m_0 / m_f), governs the maneuver budget for the descent burn. With a hydrazine thruster exhausting at roughly 2.2 km/s, Tianwen-2 has only a few hundred meters per second of total Δv available for the rendezvous, descent, sampling, and escape sequence combined. Each kilogram of mass the spacecraft sheds by venting or by jettisoning a sampling arm after contact translates directly into extra Δv headroom on the way home.

The anchor-and-attach method sidesteps some of that timing pressure. The arms can latch onto a boulder and ride the rotation with the asteroid for one full spin, giving the sampling drill time to work without the spacecraft having to hover. For both methods, the engineering constraint is the same: a few hundred grams of regolith, in a sealed capsule, must survive the return trip.

After the samples are sealed, Tianwen-2 will swing by the Moon for a gravity assist — adding roughly 1 km/s of heliocentric velocity for a negligible fuel cost — and aim for an Earth return in November 2027. If the capsule lands intact, the lab work begins: isotope ratios, cosmic-ray exposure ages, mineralogy. For the lunar-ejecta camp, the smoking gun would be a sample’s oxygen isotope signature falling outside the range of known meteorites and inside the range of lunar rocks. For the Flora-family camp, the clincher would be cosmic-ray exposure ages older than any plausible lunar crater’s age.

Either answer is interesting. A confirmed lunar origin would make Kamoʻoalewa the first known natural sample of the Moon without ever landing there, and would let planetary scientists calibrate impact-ejection dynamics with real data rather than simulations. A confirmed main-belt origin would rewrite the textbook on how quasi-satellites are captured and how space weathering proceeds on small bodies. By late 2028, with luck and a soft landing in Inner Mongolia, we will know which way the cosmic dice rolled when this little fragment came tumbling into Earth’s neighborhood. Until then, the new images are already doing their job: they have made an abstract orbital curiosity into a place with a shape, a spin, and a surface.

SpaceX filed confidentially with the U.S. Securities and Exchange Commission in early April 2026, setting in motion a process that could result in the largest initial public offering in market history. The filing, reported on April 1 by Bloomberg, Reuters, and CNBC, confirmed months of speculation about the timing of SpaceX’s transition from private to public ownership. The company, privately held since its founding in 2002, has grown into the world’s dominant commercial launch provider while operating as a closely controlled enterprise with no external public shareholders.

The confidential nature of the filing is standard procedure for companies testing the waters before a formal public offering. SpaceX submitted the paperwork under Jumpstart Our Business Startups Act provisions that allow emerging growth companies to keep their S-1 registration statements private during the SEC review period. The approach gives the company time to gauge institutional investor interest before committing to the full disclosure required for a public listing. The initial public filing is expected to become public between late April and mid-May 2026, with the roadshow to pitch the company to investors projected for early June.

The scale of the offering, if reports prove accurate, would be unprecedented in the aerospace sector. SpaceX is targeting a valuation between $1.75 trillion and $2 trillion, with plans to raise $50 to $75 billion in new capital. By comparison, Saudi Aramco’s 2019 IPO raised $29.4 billion at a valuation of approximately $1.7 trillion, making it the largest in history. The numbers reflect the extraordinary growth trajectory of a company that generated an estimated $16 to $18 billion in revenue during 2025, driven primarily by the Starlink satellite internet constellation that now serves millions of subscribers worldwide.

Financial details emerging from the preparation phase reveal a business that has transformed from a launch provider into an integrated space services company. Starlink revenue reportedly grew 842 percent over two years, reaching approximately $4.4 billion in the most recent annual period, according to data cited in multiple financial reports. The launch services division, while profitable, represents a smaller share of revenue than the constellation business, which has scaled to over 7,000 operational satellites and coverage across dozens of countries. SpaceX refinanced $20 billion in debt ahead of the IPO filing, positioning the balance sheet for public market scrutiny.

The ownership structure preserves founder Elon Musk’s control over the company after the IPO. SpaceX will issue super-voting shares that give Musk and insider investors effective control over board decisions, allowing the company to maintain its “controlled company” status under stock exchange rules. This structure is common in technology companies where founders seek public capital without surrendering operational authority. Musk’s other company, Tesla, operates under a similar dual-class structure that has kept Musk as the dominant voice in corporate governance despite owning a minority of shares.

The decision to go public arrives at a time when SpaceX’s operational momentum is at a peak. The company has conducted over 60 orbital launches already in 2026, with the Falcon 9 fleet achieving reuse milestones that validate the economic model underlying the IPO valuation. Booster B1067 reached 34 flights in late March 2026, demonstrating that hardware can sustain repeated use far beyond initial design expectations. Starship, the next-generation heavy-lift vehicle, continues its test program, with Flight 12 targeting early May 2026 from Starbase in Texas using the first Block 3 hardware configuration.

The integration of xAI into SpaceX, completed in February 2026, adds another dimension to the IPO narrative. The merger, reportedly valued at $60 billion, brings together SpaceX’s launch and satellite infrastructure with xAI’s artificial intelligence capabilities. The combined entity positions itself as an integrated space and intelligence company, potentially serving both commercial and government customers with combined hardware and AI services. Whether public market investors will assign premium valuations to this combination remains to be seen.

For the aerospace industry broadly, a public SpaceX could reshape competitive dynamics. United Launch Alliance, Blue Origin, and Rocket Lab all operate as private companies, and the success or failure of SpaceX’s public offering will signal whether capital markets view space infrastructure as a growth sector worthy of mainstream investment. The company’s stated intentions include 100 Starship launches per year, a Starlink constellation expansion to tens of thousands of satellites, and eventual crewed missions to Mars. The capital requirements for these ambitions are measured in tens of billions of dollars, which a public equity offering could help address.

The timeline for the actual listing remains subject to market conditions. The roadshow and SEC review process typically span several months, and market volatility could push the debut to late 2026 or 2027. The company has not confirmed specific listing dates, and reports from anonymous sources cited in financial coverage carry the caveat that plans can shift based on regulatory feedback or changing market sentiment. Investors seeking pre-IPO exposure have limited options through secondary markets, but those platforms trade at prices that imply valuations already near the reported IPO targets.

SpaceX’s IPO valuation rests substantially on the economics of rocket reusability, a concept that the company has spent a decade turning from theoretical to operational. The Falcon 9 booster fleet has now accumulated over 600 successful landings and 560 reflights, demonstrating that the same hardware can sustain multiple missions with periodic refurbishment. Each reflight avoids the cost of manufacturing a new booster, estimated at 30 to 40 percent of the approximately $74 million launch price.

The marginal cost of each additional reflight reflects declining refurbishment needs as the fleet matures. Early boosters required extensive inspections and part replacements after each flight. Current boosters, with thousands of flights of operational data, have undergone multiple design iterations that reduce wear and extend service life. The Merlin engines, which experience the most severe thermal and mechanical stress, have been modified between flights to reduce carbon buildup and improve tolerance to repeated firing cycles.

Starlink revenue changes the economic calculus by providing a captive launch customer that reduces dependence on external commercial contracts. When SpaceX launches Starlink satellites, it does so at internal cost rather than market price, effectively subsidizing constellation growth with launch profits from external customers. The combined business allows SpaceX to grow both its infrastructure and its customer base simultaneously, something that has not been possible for traditional launch providers constrained by smaller manifest sizes.

The valuation multiples implied by the reported IPO targets exceed those of comparable aerospace and satellite companies by substantial margins. Traditional aerospace companies trade at price-to-revenue ratios of 1.5 to 3 times, reflecting slow growth and dependent on government contracts. SpaceX’s reported revenue and growth rates, if accurate, suggest a multiple closer to technology companies than traditional aerospace. Whether public markets will sustain that multiple depends on whether the Starlink growth curve continues and whether Starship achieves the operational scale the company has projected.

The European Space Agency’s Hera spacecraft is on course for a November 2026 rendezvous with the Didymos binary asteroid system, carrying with it the culmination of humanity’s first attempt to change the orbit of a celestial body. Launched in October 2024 aboard a SpaceX Falcon 9, Hera is now completing the final leg of its 24-month journey, having already executed a critical deep-space maneuver in February-March 2026 that refined its trajectory toward the asteroid pair.

The mission represents the follow-up to NASA’s Double Asteroid Redirection Test, which struck the moonlet Dimorphos in September 2022 at approximately 6.6 kilometers per second. That impact shortened Dimorphos’s orbital period around its parent asteroid Didymos by about 32 minutes, and that seemed dramatic until subsequent research revealed something even more significant: the entire binary system’s orbit around the Sun had actually shifted by more than 10 micrometers per second. For the first time in history, human activity had measurably altered an asteroid’s solar orbit.

Hera’s primary objective is to document what happened. The spacecraft carries three main instruments: an Asteroid Framing Camera that will map the surface in color, a thermal infrared imager to measure temperatures across the moonlet, and a laser altimeter to precisely gauge topography. The spacecraft also carries two briefcase-sized CubeSats named Milani and Juven tas that will deploy once Hera arrives at Didymos. Milani will analyze surface composition using spectroscopy, while Juven tas will attempt a landing on Dimorphos to measure subsurface density using ground-penetrating radar.

When Hera enters orbit around Didymos in late 2026, it will begin mapping the impact crater created by DART. The spacecraft will approach to within a few hundred meters of the asteroid, close enough to produce images with 10-centimeter resolution. This close proximity work represents some of the most demanding navigation in deep space, requiring software that can reconstruct the environment from cameras and sensors in real-time.

The February 2026 trajectory correction burned 123 kilograms of propellant, the largest maneuver of the mission. This burn aligned Hera for the approach phase that will bring it to Didymos in November. Ground controllers at the European Space Operations Centre in Darmstadt monitored the burn, which lasted just under three minutes and changed the spacecraft’s velocity by approximately 180 meters per second.

Data from Hera will inform future planetary defense strategies. The kinetic impactor technique demonstrated by DART works, but questions remain about exactly how efficiently momentum transfers from an impact to an asteroid. The density and porosity of the target affect outcomes significantly. If an asteroid is rubble-pile in structure, held together by its own gravity, impact energy spreads differently than if it were solid rock. Hera will answer these questions.

When a spacecraft collides with an asteroid, the resulting deflection depends on several factors described by the momentum equation p = mv, where momentum equals mass times velocity. The spacecraft carries momentum equal to its mass multiplied by its impact velocity. But the asteroid also receives momentum from ejected material accelerated away from the impact site. This “bonus” momentum from ejecta can substantially exceed the spacecraft’s incoming momentum, sometimes doubling or even tripling the effective deflection.

The efficiency is measured by beta, a factor indicating how much more effective the impact is than the spacecraft alone. DART achieved a beta of approximately 2.5, meaning the deflection was 2.5 times what the spacecraft’s momentum alone would predict. Hera will measure beta more precisely, enabling accurate predictions for real threat scenarios.

The challenge for future missions is timing. A deflection works best when performed years in advance, as even a small velocity change accumulates over multiple orbits. The earlier the intervention, the less delta-v is required. For an asteroid discovered decades before potential impact, a gentle push could suffice where a late intervention might require unprecedented velocities.

Japan’s ambitious mission to explore the moons of Mars is entering its final phase of preparation at the Tanegashima Space Center, with launch targeted for the latter half of 2026 aboard the country’s H3 rocket. The Martian Moons eXploration, or MMX, represents one of the most complex interplanetary missions ever undertaken by the Japan Aerospace Exploration Agency, combining multiple scientific objectives with demanding navigation and operations in the relatively unexplored environment around the Red Planet’s two small moons, Phobos and Deimos.

The spacecraft, developed by JAXA in partnership with Mitsubishi Electric and numerous international contributors, arrived at the Tanegashima Space Center in early April 2026 following its transport from Mitsubishi Electric’s manufacturing facilities. The spacecraft is now undergoing protoflight testing in the Spacecraft Test and Assembly Building, where engineers will verify that all systems function correctly in simulated space conditions before committing to launch. This testing phase represents the final major milestone before the mission receives its launch window confirmation.

The scientific objectives of MMX address fundamental questions about the origin and evolution of Mars and its moons. Phobos and Deimos, with their irregular shapes and relatively low densities, have long puzzled planetary scientists. Several competing theories suggest they could be captured asteroids, remnants of a disrupted moon, or debris from a giant impact on Mars. MMX carries instruments designed to determine which hypothesis is correct by characterizing the moons’ composition, internal structure, and surface geology in unprecedented detail.

The spacecraft is equipped with a suite of scientific instruments from multiple space agencies. NASA’s contribution includes a neutron spectrometer and a gamma-ray spectrometer that will measure the elemental composition of the moon surfaces. The European Space Agency provides a hyperspectral camera system capable of mapping mineral distributions across the moons’ surfaces. France’s CNES contributed the microphone instrument, which will attempt to detect seismic signals from marsquakes transmitted through the moons themselves. Germany and Italy round out the international partnership with additional sensors and support systems.

One of the most ambitious elements of the mission involves a small rover that will land on Phobos and explore its surface. The rover, designed with contributions from both JAXA and the German Aerospace Center, uses a hopping mobility system that allows it to traverse the low-gravity environment of the moon, where conventional wheeled rovers would struggle. The rover carries instruments to analyze the composition of Phobos regolith and will collect samples for return to Earth.

The sample return component of MMX represents a critical capability that has not been attempted at Mars since the Soviet Union’s Phobos 2 mission in the 1980s. The mission plans to collect surface material from Phobos using a pneumatic sampling system and return it to Earth aboard a dedicated return capsule. The samples will be analyzed in laboratories worldwide, where researchers can apply the full range of analytical techniques impossible to duplicate with remote sensing instruments.

The navigation challenges of MMX are substantial. The spacecraft must arrive at Mars during a specific window when the orbital geometries allow efficient insertion into Mars orbit and subsequent approach to Phobos. The moon orbits at only approximately 6,000 kilometers above the Martian surface, placing it well within the planet’s gravitational influence. Maintaining a stable orbit around this small body requires precise understanding of its gravitational field, which scientists have been refinement through analysis of data from previous Mars missions.

The mission timeline calls for approximately one year of operations at Mars, beginning with a period of remote observation from Mars orbit before any descent attempts. During this reconnaissance phase, the spacecraft will map the surface of Phobos to identify safe landing sites and scientific targets of interest. The descent and landing operations will occur during a subsequent phase, with the rover deployment following successful touchdown.

Phobos, the larger of Mars’s two moons, measures approximately 22.4 kilometers in its longest dimension, making it one of the smaller objects ever orbited by a spacecraft. The moon’s gravitational acceleration at its surface is only approximately 0.008 meters per second squared, less than one thousandth of Earth’s surface gravity. This weak gravitational field presents unique challenges for orbital operations.

A spacecraft orbiting such a small body experiences perturbations from multiple sources. Mars’s gravitational influence dominates the orbital dynamics, causing the spacecraft’s orbit to precess rapidly. The irregular shape of Phobos creates variations in gravitational acceleration across the moon, which can cause orbital instability if the spacecraft approaches too closely. The MMX mission plans to operate at orbital distances that balance scientific observation needs against navigation safety.

The low-gravity environment also affects how the spacecraft must approach for landing. A simple descent trajectory would require constant thrust to avoid accelerating into the surface, unlike landing on larger bodies where ballistic trajectories are possible. The MMX spacecraft uses a combination of chemical propulsion and gravity-turn guidance to achieve controlled descents to the moon’s surface.